1. Field of the Invention
This invention pertains to welding machines, and more particularly to apparatus that manually regulates and visually indicates the output amperage of shunt controlled welding machines.
2. Description of the Prior Art
The output of some welding machines is regulated by a shunt that moves into and out of a transformer inside the welding machine case. The shunt is typically designed to be moved by a screw and nut arrangement. One end of a shaft protrudes through a first case panel and has a crank attached to it. The other end of the shaft has threads that mate with a nut on the shunt. Manually turning the crank causes the shunt to move linearly within the case. Examples of prior welding machines that employ a shunt and crank regulating system may be seen in U.S. Pat. Nos. 5,639,392 and 5,660,749. A generally similar welding machine is manufactured by Miller Electric Company, Appleton, Wis., under the trademark Thunderbolt.
To determine the shunt position relative to the transformer, and thus indicate the welding machine output amperage, it is known to include a wiper that is attached to the shunt. The wiper moves linearly inside the welding machine case with the shunt in response to turning the crank mounted on a shaft protruding from a first panel of the machine case. An elongated opening through a second panel of the machine case at a right angle to the first panel enables a person to see the wiper position. A scale on the outside of the case second panel adjacent the opening provides correlation between the shunt position and the welding machine output.
In another shunt controlled welding machine, there is an elongated rectangular opening in the same panel through which the crank shaft protrudes. The opening is at some distance from the crank. A long flexible band is attached at one end to the shunt and at a second end to a spring. In turn, the spring is connected to a stationary part of the welding machine. Manually turning the crank causes the shunt to move and also causes the band to slide within the opening. The band is marked in a manner that cooperates with a linear scale adjacent the opening to indicate the welding machine output in relation to the shunt position. An example of a prior shunt controlled welding machine having a crank and linearly moving indicator band on the same panel is a machine manufactured by Miller Electric Company, Appleton, Wis., under the trademark Econo Twin.
The prior shunt controlled welding machines provide excellent performance at an economical cost. Nevertheless, it is desirable that the mechanism for indicating the welding machine output be further developed.